1. Field of the Invention
This invention relates to wire guides having a Doppler mechanism for determining in vivo flow velocity of a biological fluid. In particular, it relates to a flexible, steerable, fluid velocity measuring wire guide which is receivable in a catheter and positionable subselectively in the coronary arterial tree for diagnosing heart disease.
2. Description of the Related Art
Coronary artery disease is a common medical problem, particularly in the U.S., and often manifests itself as a constriction of stenosis in the arterial tree. Coronary artery disease can lead to increased arterial stenosis and gradual dimunition of reactive hypermic response. Because arterial disease is commonplace, it is important to properly diagnose the presence of specific lesions or vessel stenosis and to properly evaluate the efficacy of treatment of these arterial lesions.
Stenosis past the coronary ostium are not only difficult to identify and treat, but are also prime concern because of their effect on available coronary vasodilator reserve. To identify coronary disease, the arteriogram has long been used to determine the presence and extent of stenoses. Applicant's co-pending application Ser. No. 775,857 (incorporated herein by reference) discusses the inadequacies of the arteriogram as an indication of the presence and nature of coronary artery disease. See, White, et al., Interpretation of the Arteriogram, 310 New Eng. J. Med. 819-824, (1984).
Transluminal angiplasty (enlargement of the lumen of a stenotic vessel using an intravascular catether) was initiated by Dotter and Judkins in the mid-1960's. However, prior to the work of Gruentzig (mid-1970's), coronary stenoses were usually treated by open heart surgery, such as coronary artery bypass surgery. Gruentzig developed an inflatable non-elastomeric balloon mounted on a small catheter which could be introduced into the vessel across the stenoses, and then inflated with a sufficient force to enlarge the stenotic lumen. Since the pioneering work of Gruentzig in the mid-1970's, there have been significant improvements in the equipment and techniques developed for this percutaneous transluminal coronary angioplasty (PTCA) procedure. In the United States, the growth in the number of PYCA procedures being performed has been dramatic--approximately 1,000 PTCA procedures were performed in 1980 and over 100,000 procedures were performed in 1986. PTCA procedures represent a major alternative to bypass surgery and have enjoyed an increasing success rate.
Although PTCA procedures have become increasingly successful, a major cause of failures is the inability to accurately identify the regions of stenoses and to evaluate the success of the angioplasty across the stenotic vessel. That is, the arteriogram is still the prime method of identifying and evaluating the stenosis and can lead to any number of mistakes in interpretations--such as observer error, superselective injection, pulsatile injection of contrast media, total occlusion, etc. Further, angiogrpahic evaluation of the region of stenoses after the PTCA procedure is often difficult, owing to the poor defination of the vessel after angioplasty. Thus, while such coronary angioplasty techniques have been relatively successful in treating the regions of stenosis, the unreliability of the arteriogram has been a significant detraction from the efficiency of angioplasty.
Because a PTCA procedure uses a steerable guidewire to place the angioplasty balloon catheter subselectively in the coronary vessels, it would be a significant advance in the art and a major improvement over the arteriogram if a guidewire were devised which was capable of getting a direct indication of blood flow in a particular region of the coronary vessel. Further, it would be a significant advance if such a guidewire capable of measuring fluid velocity were devised which was useful in measuring velocity of other biological fluids and was easily positioned in a biological vessel of interest.